Cyclic nucleotide phosphodiesterase is the degradative activity involved in controlling the physiologically active levels of these important biological "messengers". This project proposes to separate and characterize these enzymes (there are at least three distinct forms in mammalian tissues). In addition to the determination of the physical and kinetic properties, the regulatory mechanisms which control phosphodiesterase activities in vivo will be investigated in order to define their roles in hormonal and other biological systems.